A frequency synthesizer is an electronic system for generating a desired time domain signal, which can be found in many modern devices, including radio receivers, mobile telephones, radiotelephones, walkie-talkies, CB radios, satellite receivers, GPS systems, etc. The frequency synthesizer can combine frequency multiplication, frequency division, and frequency mixing (the frequency mixing process generates sum and difference frequencies) operations to produce the desired time domain signal.
Synthesizers used in commercial radio receivers are largely based on phase-locked loops (PLLs). Many types of frequency synthesizers are available as integrated circuits, reducing cost and size. High end receivers and electronic test equipment use more sophisticated techniques, often in combination.
The frequency synthesizer comprises a phase error digitizer to calculate a phase error. FIG. 1 is a block diagram of a conventional phase error digitizer 10. The conventional phase error digitizer 10 comprises a phase comparator 120 and a type converter 140.
The phase comparator 120 compares phases of two input signals, Hsync and FBsync, and outputs a comparison output CMPOut with only one bit. The difference in phase between the two input signals is called phase error. When the phase error is zero or very small, the phases of the two input signals are equal. The type converter 140 converts the comparison output CMPOut with 1 bit to a phase error with 7 bits.
The conventional phase error digitizer is difficult to design and implement, more expensive, larger and more sensitive to voltage noise, temperature and process than an all-digital phase error digitizer. Therefore, an all-digital phase error digitizer is urgently needed.